ST STM32F207 Series Reference Manual page 60

Memory and bus architecture
Embedded bootloader
The embedded bootloader mode is used to reprogram the Flash memory using one of the
following serial interfaces:
•
USART1(PA9/PA10)
•
USART3(PB10/11 and PC10/11)
•
CAN2(PB5/13)
•
USB OTG FS(PA11/12) in Device mode (DFU: device firmware upgrade).
The USART peripherals operate at the internal 16 MHz oscillator (HSI) frequency, while the
CAN and USB OTG FS require an external clock (HSE) multiple of 1 MHz (ranging from 4 to
26 MHz).
The embedded bootloader code is located in system memory. It is programmed by ST
during production. For additional information, refer to application note AN2606.
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